1. Field of the Invention
The invention relates to a waveguide system with a differential waveguide. Waveguide systems of this kind are required, for example, for the transmission of a test signal from a probe to a measuring instrument, for example, a spectrum analyzer, a network analyzer or an oscilloscope.
2. Related Technology
A waveguide system with a coaxial line is known, for example, from EP 1 605 588 A2. The waveguide disclosed in this document is not a differential waveguide, but a differential signal is transmitted via two separate coaxial lines and then supplied to an operational amplifier acting as an input amplifier. An input network is disposed at the front-end of each coaxial line, and a terminating network is disposed at the rear end of each coaxial line facing towards the operational amplifier. The networks are formed by ohmic resistors and capacitors.
One disadvantage of the two de-coupled, grounded waveguides according to EP 1 605 588 A2 is that a relatively-large structure is present, and the handling of the two cables by the user is awkward and impracticable. Moreover, in practice, it is difficult to manufacture two individual waveguides of exactly the same length. Even 1 mm difference in length leads to a time displacement of the differential signals relative to one another by approximately 5 ps. In the case of typical signals with a build-up time of 35 ps (equivalent to 10 GHz bandwidth), this leads to considerable signal distortions and transition from common mode to differential mode and vice versa. Moreover, with the two grounded lines, it is difficult to connect the grounds to one another at both ends with low-inductance. In general, this can only be achieved in an inadequate manner, which means that the differential current at the cable input cannot flow freely, and undesirable external modes are excited.